1. Field of the Invention
The present invention relates to a phased array antenna and related method; and more particularly, to the architecture and related method of a phased array antenna for controlling the aperture illumination of a radiated beam.
2. Discussion of Related Art
Phased array antennae may be classified as either being an active array antenna or a passive array antenna. Passive arrays typically do not provide selectable weighting since the weighting of the aperture is established by the mechanical dimensions and the characteristics of the manifolds upon manufacture. Typically, the manifold of a passive array routes the appropriate microwave power to the individual phase shifters and radiators with very little loss. Routing the correct power at the appropriate phase to the radiator determines the aperture weighting.
Active arrays are being proposed with selectable weighting of the apertures, but in a manner which results in very significant performance penalties. For example, most or all of the elements are sized to generate the same RF power via local dedicated power amplifiers. Although this arrangement is efficient and cost effective with respect to the manufacture of the amplifiers, it is most advantageous for arrays where the apertures are uniformly illuminated or arrays with uniform illumination in the center of the array and less power around the periphery, such as trapezoidal or step tapers, for example. Conventional active antenna arrays that utilize low sidelobe weighting, such as 45 dB Taylor weight, results in significant performance degradation because much of the power is attenuated or lost, rather than being redistributed, as is the case of the passive antenna array. For example, attenuating from a uniform weighting to a heavy Taylor weighting results in a 6 dB power loss in addition to the inevitable taper loss of about 1.5 dB. The six dB power loss represents a significant degradation in radar range performance and is a serious shortcoming of the active array concept.